Beyond being a great way to rebound post-workout, smoothies seem like the epitome of a healthy snack. They've got fruit, are easy to make on busy days, and are endlessly customizable so you can basically never get bored. But the truth is that even though smoothies definitely can be part of your healthy-eating arsenal, they can also secretly be calorie and sugar bombs. Calorie-laden desserts certainly aren't evil—sometimes it seems like they make life worth living. But it's kind of annoying when you think you're having something healthy that's practically a dessert in disguise, especially if you're attempting to lose weight. Here, eight things you should know about smoothies if you've got a weight-loss goal in mind.

1. Fruit is great for you, but it can also have a lot of calories and sugar—so if you’re trying to lose weight, you’ll want to watch portion sizes.

Even though fruit is healthy, tipping a boatload of it into your blender can be a bad thing. "Fruits' sugars are natural, but they still add up," Brigitte Zeitlin, M.P.H., R.D., C.D.N., founder of the New York-based BZ Nutrition, tells SELF. Fruit usually contains both fructose and glucose, the latter of which makes up carbohydrates, meaning it gives you energy. Even though fruit doesn't have sucrose, or table sugar, too much of any kind of sugar can turn into fat, and over the long-term, it can potentially predispose you to diabetes and other chronic illnesses. Zeitlin recommends sticking to one serving of fruit per smoothie, which means one cup. That will help you keep your smoothies around 250 calories—much more than that, and you're getting into meal territory.

2. Getting enough fiber is part of building a truly satiating smoothie.

"Fiber is key to staying full for long periods of time, so it wards off unnecessary snacking between meals," says Zeitlin. When your smoothies don't have enough of this essential nutrient, you may start overcompensating with extra fruit or grab a side snack along with your smoothie. To make sure your smoothie comes in at Zeitlin's recommended five to eight grams of fiber, use fruit that still has its skin (the most fiber-rich part), like strawberries, apples, and pears. You can also load up on as many vegetables like kale and spinach as you like.

3. If you skimp on protein, you might find yourself hungry again before it's time for your next meal.

Just like fiber, your smoothie won't be filling if you don't get enough protein. Plus, there's the fact that when you drink instead of chew, it's harder to eat mindfully and help flood your body with satiety cues. That makes getting enough protein extra important—if you don't, you might be hungry and need to eat more later, accidentally taking in more calories than you intended. Zeitlin recommends aiming for around 10 grams of protein per smoothie. Consider adding something like two tablespoons of nut butter, which has around seven grams, or a half-cup of plain Greek yogurt, which has around 12.

"Canned fruit is sitting in sugar water," says Zeitlin. Instead, turn to fresh or frozen fruit to get your fix. "I'll often use frozen berries in my smoothies because I'm processing them anyway, then eat fresh fruit as snacks," says Zeitlin. And if you're worried that frozen fruit is lacking, don't worry: it's often flash frozen, meaning you won't miss out on nutrients.

5. Sweeteners are perfect when you're looking for a treat, but they can affect your smoothie's calorie count.

Agave. Honey. Maple syrup. Juice. All delicious, to be sure. But they often make your smoothie's calories skyrocket, especially if you're not measuring out your portions. Luckily, they're often not really necessary. "Smoothies should be naturally sweet from the fresh or frozen fruit you're including," says Zeitlin. If you still feel like your smoothies are missing that extra layer of flavor, consider adding spices like cinnamon and nutmeg or a few drops of vanilla extract.

6. Unsweetened milk substitutes have less sugar and calories, so they can be a better choice for weight loss.

7. Making smoothies instead of ordering them at health shops is an easy way to keep tabs on exactly what you're drinking.

Trendy smoothie and juice shops are sprouting up all over, and many of them do actually use healthy ingredients. The problem is that unless you're the one making your smoothie, you can't control the portions. Even if they employees are great at ballparking it, you can never be sure of exactly what you're drinking. "The best way to make sure your portions are in check is to make your own smoothies at home," says Zeitlin.

They often only seem good for you. "Look at the ingredients label, because these usually have way too much sugar in them," says Zeitlin. And those sugars often don't just come from fruits, because packaged smoothies likely have added sugar in them as well. If it seems like the smoothie is mostly vegetables, less than 250 calories, and doesn't have a ton of sugar, check the serving size. "One bottle might have two or three servings," says Zeitlin.